a) Field of the Invention
The invention concerns a wind power installation comprising a rotor with at least one rotor blade for converting the kinetic energy of the wind into mechanical energy, an adjusting device for individual adjustment of at least one rotor blade, a generator for converting the mechanical energy of the rotor into electrical energy, and an operative connection between the rotor and the generator for transmitting the mechanical energy of the rotor to the generator.
b) Description of the Related Art
Wind power installations of that kind are part of the state of the art. Thus for example the German reference book xe2x80x98Windkraftanlagenxe2x80x99 by Erich Hau, Springer-Verlag, 2nd edition, 1996, pages 52, 175, 222 to 242, 269 and 320 shows wind power installations of that kind. In those known wind power installations, the speed of rotor rotation and the power output can be regulated by means of a regulating system for the angle of incidence of the rotor blade. In addition the known system for regulating the rotor blade angle of incidence serves to protect the rotor from rotating at an excessive speed in the event of high wind speeds or in the event of a mains failure in which the generator torque abruptly disappears. Both cases involve protecting the wind power installation from damage due to a rotor rotating at an excessively high speed.
In that respect there are essentially two ways of producing a reduction in the speed of rotor rotation, by means of rotor blade adjustment; on the one hand the blade setting angle can be reduced in the direction of smaller aerodynamic angles of incidence in order thereby to reduce the power consumption of he rotor. On the other hand, it is possible to achieve the critical aerodynamic angle of incidence, the so-called stall condition, by adjusting the rotor blade setting angle to larger angles. The latter option affords the advantage of adjustment in a shorter distance, but it entails the disadvantage that flow break-down (stall) is related to high loadings for the rotor and the entire wind power installation. A common aspect of both adjustment options however, is that they only take account of a mean wind speed acting on the entire wind power installation, or a certain limit speed of rotor rotation, as the starting signal for setting the rotor blade angle.
A known wind power installation is installed in GB-A-2 067 247. In accordance with that publication, the wind power is measured in the plane of the rotor of wind power installations by means of pressure probes which are disposed at the surface of the rotor blades in the proximity of the profile nose. In that publication, the measurement values ascertained in that way are used inter alia to pivot the rotor plane of a wind power installation until the measurement values are the same for a rotor position of 90xc2x0 and 270xc2x0.
A further known wind power installation is known from U.S. Pat. No. 4,297,076. The wind turbine disclosed here is a stall-controlled machine. The main rotor blades of that known installation are fixedly connected to the hub and are not rotatable on their longitudinal axis. The main loads in the main shaft of the installation are produced by the non-rotatable components of the rotor blades.
The above mentioned options in the state of the art do not take account of the fact that, particularly when a large rotor diameter is involved, there can be a non-uniform distribution of the wind conditions over the area of the rotor. That in turn results in different loadings on individual rotor blades as well as asymmetrical loadings for the drive train of the wind power installation, that is to say the hub, the drive shaft and the respective bearings. Different asymmetrical loadings of that kind, however do not only occur just as from a given speed of rotor rotation or a given wind speed, but also take place continuously during normal operation of the wind power installation. The blade angle regulation known hitherto from the state of the art cannot therefore react to fluctuations in wind speed and fluctuations in load, which are related thereto, in the region of the rotor, as the known installations provide for uniform, synchronous adjustment of the rotor blades.
In more modern installations (see in particular page 238 of the above-mentioned reference book), on the one hand, individual electrical adjustment of each individual rotor blade has admittedly been proposed; however that proposal is also based on the assumption of a mean wind speed acting on the wind power installation. With that and the further assumption that the wind speed increases with height, the proposal is then for a fixed, rotationally cyclical correction of the rotor blade incidence angle in order to be able to at least partially regulate out the changing loads upon the increase in wind speed with height. That rotor blade setting procedure also suffers from the disadvantage that the angle of incidence of the rotor blades is fixedly predetermined and therefore cannot react to local, temporary changes in the wind speed over a part of the rotor. With this proposal also therefore, there is an asymmetrical loading on the components of the wind power installation, which thus reduces the service life thereof, in the case of local peaks in the wind speed as viewed over the area of the rotor.
Primary object of the invention is therefore that of avoiding the above-mentioned problems and providing a wind power installation which reduces the loadings which can occur by virtue of local, temporary peaks in the wind speed in portions of the rotor area.
In accordance with the invention, that object is attained in that, in a wind power installation of the kind set forth in the opening part of this specification, there are provided measuring means for ascertaining the instantaneous loading of a part of the wind power installation, control means for ascertaining a position of at least one rotor blade, wanted for the instantaneous loading, and for suitably adjusting the rotor blade by means of the adjusting device, and connecting means connecting the adjusting device and the measuring means to the control means.
The wind power installation according to the invention makes it possible, by means of the adjusting device for individual adjustment of at least one rotor blade, for the wind power installation to be matched by means of the control means to instantaneous loadings which occur locally only at a part of the wind power installation, such loadings being ascertained by the measuring means. This advantageously provides that local peaks in the loading on the rotor blades, the hub, the shaft drive and the bearings used are avoided. That in turn has the consequence that the service life of the wind power installation is increased or is not unintentionally reduced as asymmetrical loadings of parts of the wind power installation, which are such as to reduce the service life thereof, are substantially avoided.
In addition, the wind power installation according to the invention permits optimum use to be made of the instantaneous distribution of the wind speeds on the rotor area and thus makes it possible to contribute to an increased power output from the wind power installation as all rotor blades are always operated with the desired and thus optimum blade angle and therefore the level of efficiency per rotor blade rises in comparison within the efficiency of the wind power installations in the state of the art.
It is particularly preferred for the position of the rotor blade or blades to be uninterruptedly adapted to the instantaneous loading of the wind power installation. In that way it is possible to ensure that the wind power installation is continually operated in the optimum working range and at the same time is protected from loading peaks, triggered due to wind speed peaks which occur locally in the region of the rotor.
In a preferred embodiment of the invention the measuring means for ascertaining the local loading on a rotor blade ascertain a wind speed which obtains at the rotor blade. For that purpose the measuring means preferably have an anemometer mounted on the rotor blade. By virtue of the fact that the anemometer is arranged directly on the rotor blade, it is possible to achieve highly accurate control of the angular positioning of the rotor blade, as a reaction to an increased or lower wind speed. For, measurement of the wind speed directly at the location at which adjustment of the wind power installation also occurs, namely directly at the rotor blade to be adjusted, permits rapid accurate adaptation of the angular position of the rotor blade to local variations in the wind speed.
A further preferred embodiment is distinguished in that the measuring means ascertain a mechanical load which prevails in a portion of the region of the rotor. In this embodiment, direct ascertainment of the mechanical loading occurring in a portion of the rotor provides the control means with precise information, by means of which the control means can ascertain a desired position of at least one adjustable rotor blade, having regard to the predetermined data in respect of geometry, load and/or material.
It is particularly advantageous in this embodiment if the measuring means ascertain a mechanical load which prevails in the adjustable rotor blade. For, by the load being ascertained directly in the rotor blade, very precise information about the wind strength profile over the area of the rotor can be obtained, in a similar manner to the above-discussed procedure for directly ascertaining the wind speed at the rotor blade. With such precise information, the control means are then capable of controlling a particularly accurate reaction on the part of the adjusting device so that an existing load peak in a portion of the rotor can be very rapidly reduced.
A further embodiment of the invention with a rotor hub for carrying the rotor blades has measuring means which measure a mechanical load occurring in the rotor hub. This embodiment also permits rapid adaptation of the rotor blades to the altered load situation. The same applies for embodiments with a stub shaft or spindle portion for supporting the rotor, in which the measuring means ascertain a load prevailing in the stub shaft, and in the case of a wind power installation having a drive shaft which connects the rotor and the generator together directly or by way of a transmission, wherein the measuring means ascertain a load which prevails in the drive shaft or in the bearings of the drive shaft or the stub shaft or spindle portion. All the above-mentioned embodiments permit accurate detection of the local load conditions in the region of the rotor and thus accurate control of the adjusting device by means of the control means. In that respect it is particularly preferred if the measuring means, for measuring the mechanical load, have strain gauges which are mounted on the respective loaded parts of the wind power installation. That means that the strain gauges can be mounted on the rotor blade, in the interior of the rotor blade, on the rotor hub or in the interior of the rotor hub, on the stub shaft or in the interior of the stub shaft, on the drive shaft or in the interior of the drive shaft, or at the bearings. In all the above-indicated different manners of mounting the strain gauges, it is possible easily to determine the mechanical loading involved and thus individually adjust the rotor blade in accordance with the invention.
A further preferred embodiment of the invention has measuring means which ascertain an afflux angle of the wind, which prevails at the rotor blade to be adjusted. By virtue thereof it is advantageously possible also to determine the wind direction of the afflux flow of wind relative to the rotor blade to be adjusted. By means of that measurement value, the control means can also react to a change in wind direction which occurs in a portion of the rotor.
Particularly in conjunction with the above-mentioned load-measuring means, the control means have a very accurate picture about the instantaneous wind conditions over the area of the rotor: by virtue of the load-measuring means the control means can take account of an absolutely occurring load and in addition by virtue of the measuring means for determining the afflux anglexe2x80x94having regard to the actual rotor blade positionxe2x80x94it is also possible to provide for accurate determination of the magnitude of the angle to be adjusted. Accurate adaptation with wind conditions which change quickly is thus advantageously ensured by the combined use of afflux angle measurement and load measurement in the rotor blades. In that respect it is particularly preferred for measurement of the afflux angle to be effected by a wind vane or indicator mounted on the rotor blade.
A further preferred embodiment of the invention is distinguished in that a portion of a rotor blade is adjustable asynchronously relative to at least one further adjustable portion of another rotor blade. Thus, particularly when dealing with large rotor diameters, it is possible to reduce the level of apparatus structure and expenditure insofar as preferably the outer portion of the rotor blade is adapted to be adjustable, as power generation of the rotor is substantially concentrated on the outer blade region.
In an advantageous embodiment of the invention, the position of the rotor blade or blades, which is desired for a given instantaneous loading, can be predetermined by way of input means connected to the control means. In that way the wind power installation according to the invention can be adapted on site after erection to possibly unforeseen wind conditions or after repair to modified material sizes or modified rotor blade profiles.
It has been found particularly advantageous for the actual value of the rotor blade angular position to be detected by an adjusting transmission which, together with an adjusting motor, forms the adjusting device. In that respect, it is particularly advantageous if the control means effect adjustment of the rotor blade practically simultaneously with detection of the measurement values from the strain gauges, the anemometer or the wind vane or indicator, after comparison with the actual value of the adjusting drive, by means of the adjusting motor. Such an instantaneous reaction to changes in loading in the region of the rotor blades ensures that harmful loadings or one-sided loadings on the rotor are effectively avoided.
An advantageous process for the adaptation of a wind power installation to instantaneous loadings which prevail only in a local portion of the wind power installation is distinguished in that the instantaneous loading of a part of the wind power installation is detected by measuring means and a position of at least one of the rotor blades, which is desired for the instantaneous loading, is ascertained by control means, and that the rotor blade is suitably adjusted by means of the adjusting device, wherein the adjusting device and the measuring means are connected to the control means by way of connecting means. That simple process makes it possible to achieve an effective increase in the service life and efficiency of the wind power installation according to the invention.
Further advantageous configurations of the invention are set forth in the appendant claims.